Document Type

Article

Publication Date

2016

Publication Title

Atmospheric Chemistry and Physics

ISSN

1680-7316

Volume

16

Issue

14

First Page

9019

Last Page

9045

DOI

http://dx.doi.org/10.5194/acp-16-9019-2016

Abstract

Megacities are major sources of anthropogenic fossil fuel CO2 (FFCO2) emissions. The spatial extents of these large urban systems cover areas of 10 000 km2 or more with complex topography and changing landscapes. We present a high-resolution land–atmosphere modelling system for urban CO2 emissions over the Los Angeles (LA) megacity area. The Weather Research and Forecasting (WRF)-Chem model was coupled to a very high-resolution FFCO2 emission product, Hestia-LA, to simulate atmospheric CO2 concentrations across the LA megacity at spatial resolutions as fine as  ∼  1 km. We evaluated multiple WRF configurations, selecting one that minimized errors in wind speed, wind direction, and boundary layer height as evaluated by its performance against meteorological data collected during the CalNex-LA campaign (May–June 2010). Our results show no significant difference between moderate-resolution (4 km) and high-resolution (1.3 km) simulations when evaluated against surface meteorological data, but the high-resolution configurations better resolved planetary boundary layer heights and vertical gradients in the horizontal mean winds. We coupled our WRF configuration with the Vulcan 2.2 (10 km resolution) and Hestia-LA (1.3 km resolution) fossil fuel CO2 emission products to evaluate the impact of the spatial resolution of the CO2 emission products and the meteorological transport model on the representation of spatiotemporal variability in simulated atmospheric CO2 concentrations. We find that high spatial resolution in the fossil fuel CO2 emissions is more important than in the atmospheric model to capture CO2 concentration variability across the LA megacity. Finally, we present a novel approach that employs simultaneous correlations of the simulated atmospheric CO2 fields to qualitatively evaluate the greenhouse gas measurement network over the LA megacity. Spatial correlations in the atmospheric CO2 fields reflect the coverage of individual measurement sites when a statistically significant number of sites observe emissions from a specific source or location. We conclude that elevated atmospheric CO2 concentrations over the LA megacity are composed of multiple fine-scale plumes rather than a single homogenous urban dome. Furthermore, we conclude that FFCO2 emissions monitoring in the LA megacity requires FFCO2 emissions modelling with  ∼  1 km resolution because coarser-resolution emissions modelling tends to overestimate the observational constraints on the emissions estimates.

Comments

S. Feng (JIFRESSE, University of California, Los Angeles, Los Angeles, CA, USA)
S. Feng (Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA)
S. Feng (now at: Department of Meteorology and Atmospheric Science, Pennsylvania State University, University Park, PA, USA)
T. Lauvaux (Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA)
T. Lauvaux (Department of Meteorology and Atmospheric Science, Pennsylvania State University, State College, PA, USA)
S. Newman (Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA, USA)
P. Rao (Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA)
R. Ahmadov (Cooperative Institute for Research in Environmental Sciences, University of Colorado at Boulder, Boulder, CO, USA)
R. Ahmadov (Earth System Research Laboratory, National Oceanic and Atmospheric Administration, Boulder, CO, USA)
A. Deng (Department of Meteorology and Atmospheric Science, Pennsylvania State University, State College, PA, USA)
L. I. Díaz-Isaac (Department of Meteorology and Atmospheric Science, Pennsylvania State University, State College, PA, USA)
R. M. Duren (Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA)
M. L. Fischer (Lawrence Berkeley National Laboratory, Berkeley, CA, USA)
C. Gerbig (Max Planck Institute for Biogeochemistry, Hans-Knöll-Str. 10, 07745 Jena, Germany)
K. R. Gurney (School of Life Science, Arizona State University, Tempe, AZ, USA)
J. Huang (School of Life Science, Arizona State University, Tempe, AZ, USA)
S. Jeong (Lawrence Berkeley National Laboratory, Berkeley, CA, USA)
Z. Li (Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA)
C. E. Miller (Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA)
D. O'Keeffe (School of Life Science, Arizona State University, Tempe, AZ, USA)
R. Patarasuk (School of Life Science, Arizona State University, Tempe, AZ, USA)
S. P. Sander (Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA)
Y. Song (School of Life Science, Arizona State University, Tempe, AZ, USA)
K. W. Wong (Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA)
K. W. Wong (Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA, USA)
Y. L. Yung (Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA, USA)

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